Method for driving a converter and its ANPC circuit

Abstract

This application provides a converter and a driving method for its ANPC circuit. According to the driving method of the ANPC circuit, first, with the aim of enabling the ANPC circuit in the converter to bear the switching loss using the internal transistor and the external transistor respectively in two half-switching periods of the switching cycle, the output state switching sequence of the ANPC circuit is determined. Then, based on the output state switching sequence, control signals for each switching transistor of the ANPC circuit are generated and output. Thereby, the ANPC circuit can achieve the equalization of the switching losses of the internal transistor and the external transistor. Moreover, the equalization granularity of the switching loss is a half-switching period, the equalization effect is fine, and the loss fluctuation is low.

Description

Technical Field

[0001] This application relates to the technical field of power electronics, and particularly to a converter and a driving method for its ANPC circuit.

[0002] This application claims the priority of a Chinese patent application filed with the China National Intellectual Property Administration on February 17, 2023, with the application number 202310********.6 and the invention title "Converter and Driving Method for Its ANPC Circuit", and all its contents are incorporated herein by reference.

Background Art

[0003] The ANPC (Active Neutral Point Clamped) converter uses a fully controlled switching device (and its freewheeling diode) instead of a diode to realize neutral point clamping compared with the conventional NPC (Neutral Point Clamped) converter. Thereby, it has a redundant drive distribution method, improves the degree of freedom of system control. In its single-phase topology structure, the switching tubes connected to the positive and negative poles on the DC side are called external tubes, the switching tubes connected to the AC side are called internal tubes, and the switching tubes connected to the neutral point on the DC side are called clamp tubes.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Regarding ANPC single-phase circuits, there are many drive distribution methods for its six fully controlled switching devices. Common methods include ANPC-1, where the outer tube and clamp tube operate at high frequency and the inner tube operates at the power supply frequency, and ANPC-2, where the inner tube operates at high frequency and the other transistors operate at the power supply frequency. However, in the former case, the switching loss of the outer tube is greater than that of the inner tube, and in the latter case, the switching loss of the inner tube is greater than that of the outer tube. Neither method can achieve equalization (i.e., balance) of the switching losses of the devices.

[0005] This application provides a converter and a method for driving its ANPC circuit to achieve switching loss leveling of a device. [Means for solving the problem]

[0006] To achieve the above objective, this application provides the following technical solution. A first aspect of this application provides a method for driving the ANPC circuit of a converter. With the goal of enabling the ANPC circuit of the converter to bear the switching losses by using the internal tube and the external tube, respectively, during two half-switching cycles of the switching period, the steps include determining the output state switching sequence of the ANPC circuit, The process includes the step of generating and outputting control signals for each switching tube in the ANPC circuit based on the output state switching sequence.

[0007] Preferably, the step of determining the output state switching sequence of the ANPC circuit of the converter is to enable the ANPC circuit to bear switching losses by using the internal tube and the external tube, respectively, during two half-switching cycles of the switching period, The step includes determining the zero-level output state of the output state switching sequence during two half-switching periods within the switching period of the ANPC circuit, The aforementioned zero-level output state includes a first zero-level output state in which the internal tube bears the switching loss, and a second zero-level output state in which the external tube bears the switching loss.

[0008] Preferably, before determining the output state switching sequence of the ANPC circuit, The further step includes the objective of leveling the on-state losses borne by the internal tube.

[0009] Preferably, the step of determining the output state switching sequence of the ANPC circuit of the converter is to enable the ANPC circuit to bear switching losses by using the internal tube and the external tube, respectively, during two half-switching cycles of the switching period, The step includes determining the zero-level output state of the output state switching sequence during two half-switching periods within the switching period of the ANPC circuit, The aforementioned zero-level output states include a first zero-level output state in which the internal tube bears the switching loss, a second zero-level output state in which the external tube bears the switching loss, and a third zero-level output state in which two parallel branches exist when phase current flows into or out of the bridge arm.

[0010] Preferably, in the ANPC circuit, the two external tubes are a first switching tube connected to the positive terminal on the DC side and a fourth switching tube connected to the negative terminal on the DC side, the two internal tubes are a second switching tube connected between the first switching tube and the AC side and a third switching tube connected between the AC side and the fourth switching tube, and the two clamp tubes are a fifth switching tube connected between the first switching tube and the DC side neutral point and a sixth switching tube connected between the DC side neutral point and the fourth switching tube. Within the positive half-cycle of the AC output voltage of the ANPC circuit, in the first zero-level output state, the first switching tube, the third switching tube, and the sixth switching tube are in the ON state, and the other switching tubes are in the OFF state. During the negative half-cycle of the AC output voltage of the ANPC circuit, in the first zero-level output state, the second switching tube, the fourth switching tube, and the fifth switching tube are ON, while the other switching tubes are OFF.

[0011] Preferably, in the ANPC circuit, the two external tubes are a first switching tube connected to the positive terminal on the DC side and a fourth switching tube connected to the negative terminal on the DC side, the two internal tubes are a second switching tube connected between the first switching tube and the AC side and a third switching tube connected between the AC side and the fourth switching tube, and the two clamp tubes are a fifth switching tube connected between the first switching tube and the DC side neutral point and a sixth switching tube connected between the DC side neutral point and the fourth switching tube. Within the positive half-cycle of the AC output voltage of the ANPC circuit, in the second zero-level output state, the second switching tube, the third switching tube, and the sixth switching tube are in the ON state, and the other switching tubes are in the OFF state. During the negative half-cycle of the AC output voltage of the ANPC circuit, in the second zero-level output state, the second switching tube, the third switching tube, and the fifth switching tube are ON, while the other switching tubes are OFF.

[0012] Preferably, in the ANPC circuit, the two external tubes are a first switching tube connected to the positive terminal on the DC side and a fourth switching tube connected to the negative terminal on the DC side, the two internal tubes are a second switching tube connected between the first switching tube and the AC side and a third switching tube connected between the AC side and the fourth switching tube, and the two clamp tubes are a fifth switching tube connected between the first switching tube and the DC side neutral point and a sixth switching tube connected between the DC side neutral point and the fourth switching tube. Within the positive half-cycle of the AC output voltage of the ANPC circuit, in the third zero-level output state, the third switching tube, the fifth switching tube, and the sixth switching tube are in the ON state, and the other switching tubes are in the OFF state. During the negative half-cycle of the AC output voltage of the ANPC circuit, in the third zero-level output state, the second switching tube, the fifth switching tube, and the sixth switching tube are ON, while the other switching tubes are OFF.

[0013] Preferably, the output state switching sequence is: The third zero-level output state, the first zero-level output state, a positive or negative level output state, the second zero-level output state, the third zero-level output state, or The third zero-level output state, the second zero-level output state, the positive or negative level output state, the first zero-level output state, and the third zero-level output state appear in that order.

[0014] Preferably, within the positive half-cycle of the AC output voltage of the ANPC circuit, the third zero-level output state is such that when phase current flows into the bridge arm, there are two parallel branches. In the negative half-cycle of the AC output voltage of the ANPC circuit, the third zero-level output state has two parallel branches when the phase current flows out from the bridge arm.

[0015] Preferably, the step of generating and outputting control signals for each switching tube of the ANPC circuit based on the output state switching sequence is: In each output state of the output state switching sequence, a step of generating and outputting a control signal for each switching tube based on the on / off state of each switching tube in the ANPC circuit, or, With the goal of realizing the aforementioned output state switching sequence, the method includes a step of employing a carrier comparison method to generate and output control signals for each switching tube in the ANPC circuit.

[0016] A second aspect of this application provides a converter, which includes a main circuit and a control device. The main circuit includes at least one ANPC circuit, The main circuit is controlled by the control device, which performs the method for driving the ANPC circuit of the converter described in any one of the first embodiments described above.

[0017] Preferably, the ANPC circuit includes six switching tubes. The first to fourth switching tubes are connected in series in sequence. The other end of the first switching tube is connected to the DC positive terminal of the ANPC circuit, and the other end of the fourth switching tube is connected to the DC negative terminal of the ANPC circuit, so that the first switching tube and the fourth switching tube each function as two external tubes of the ANPC circuit. The connection point between the second switching tube and the third switching tube is connected to the AC side of the ANPC circuit, and the second and third switching tubes each function as two internal tubes of the ANPC circuit. The connection point between the first switching tube and the second switching tube is connected to the DC neutral point of the ANPC circuit via the fifth switching tube, and the connection point between the third switching tube and the fourth switching tube is connected to the DC neutral point of the ANPC circuit via the sixth switching tube, with the fifth and sixth switching tubes each functioning as two clamp tubes of the ANPC circuit.

[0018] Preferably, the main circuit includes three of the ANPC circuits, The DC sides of each of the ANPC circuits are connected in parallel, and the AC side of each of the ANPC circuits is one phase of the AC side of the main circuit, respectively.

Advantages of the Invention

[0019] According to the driving method of the ANPC circuit of the converter provided by this application, first, aiming at enabling the ANPC circuit of the converter to bear the switching loss by using the internal tubes and external tubes respectively in two half-switching periods of the switching period, determine the output state switching sequence of the ANPC circuit, and then, based on the output state switching sequence, generate and output the control signals of each switching tube of the ANPC circuit. Thereby, the ANPC circuit can achieve the equalization of the switching losses of the internal tubes and external tubes, and the equalization granularity of the switching losses is a half-switching period, the equalization effect is fine, and the loss fluctuation is low.

[0020] To more clearly explain the embodiments of the present invention or the technical solutions of the prior art, the necessary drawings for describing the embodiments or the prior art are briefly introduced below. The drawings described below are only the embodiments of the present invention. On the premise that those skilled in the art do not perform labor worthy of inventive step, other drawings can be obtained based on the provided drawings.

Brief Description of the Drawings

[0021] [Figure 1] It is a topology diagram of the ANPC circuit provided by the prior art. [Figure 2] It is a schematic diagram of the driving distribution method of the ANPC circuit provided by the prior art. [Figure 3] It is a schematic diagram of another driving distribution method of the ANPC circuit provided by the prior art. [Figure 4] It is a schematic diagram of the signal waveform in the positive half-cycle of the output voltage of the driving distribution method of both modes provided by the embodiment of this application. [Figure 5]This is a schematic diagram of another signal waveform in the positive half-period of the output voltage for the dual-mode drive distribution scheme provided by the embodiment of this application. [Figure 6] This is a schematic diagram of the signal waveform during the negative half-period of the output voltage for the dual-mode drive distribution method provided in the embodiment of this application. [Figure 7] This is a schematic diagram of another signal waveform during the negative half-period of the output voltage for the dual-mode drive distribution scheme provided in the embodiment of this application. [Figure 8] This is a flowchart of the driving method for the ANPC circuit of the converter provided in the embodiment of this application. [Figure 9] This is a schematic diagram of the current path through which the phase current flows into the bridge arm in the 0+ state provided by the embodiment of this application. [Figure 10] This is a schematic diagram of the current path through which the phase current flows out of the bridge arm in the 0+ state provided by the embodiment of this application. [Figure 11] This is a schematic diagram of the current path through which the phase current flows into the bridge arm in the 0-state provided by the embodiment of this application. [Figure 12] This is a schematic diagram of the current path through which the phase current flows out of the bridge arm in the 0-state provided by the embodiment of this application. [Figure 13] This is a schematic diagram of a signal waveform that realizes the output state switching sequence 0+→0+in→P→0+out→0+ using a carrier comparison method, as provided by an embodiment of this application. [Modes for carrying out the invention]

[0022] The following describes the technical aspects of the embodiments of the present invention clearly and completely by combining the drawings of the embodiments of the present invention, and the embodiments described are not all embodiments but only a selection of embodiments of the present invention. All other embodiments obtained based on the embodiments of the present invention, provided that a person skilled in the art does not perform work worthy of inventive step, are all within the scope of protection of the present invention.

[0023] In this application, the terms “include,” “incorporate,” or any other variation thereof are intended to include non-exclusive inclusion, thereby meaning that a process, method, article, or apparatus containing a set of elements includes not only those elements but also other elements not explicitly listed, or even elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element limited by the phrase “includes XX” does not preclude a process, method, article, or apparatus containing that element from having other identical elements.

[0024] As shown in Figure 1, the ANPC circuit includes six switching tubes (S1 to S6 in the diagram), each of which is equipped with a corresponding flywheel diode (D1 to D6 in the diagram). The first to fourth switching tubes S1 to S4 are connected in series sequentially. The other end of the first switching tube S1 is connected to the DC positive terminal P of the ANPC circuit, and the other end of the fourth switching tube S4 is connected to the DC negative terminal N of the ANPC circuit. The connection point between the second switching tube S2 and the third switching tube S3 is connected to the AC side of the ANPC circuit (its output voltage is Vout). The connection point between the first switching tube S1 and the second switching tube S2 is connected to the DC neutral point O of the ANPC circuit via the fifth switching tube S5, and the connection point between the third switching tube S3 and the fourth switching tube S4 is connected to the DC neutral point O of the ANPC circuit via the sixth switching tube S6. The first switching tube S1 and the fourth switching tube S4, connected to the positive and negative terminals on the DC side (P and N in Figure 1), are called external tubes. The second switching tube S2 and the third switching tube S3, connected to the AC side, are called internal tubes. The fifth switching tube S5 and the sixth switching tube S6, connected to the DC side neutral point O, are called clamp tubes.

[0025] In the ANPC-1 drive distribution method (see Figure 2 for its drive distribution method), the external tubes (S1, S4) and clamp tubes (S5, S6) operate at high frequency, while the internal tubes (S2, S3) operate at the power supply frequency. In this case, the switching loss of the external tubes is greater than that of the internal tubes. In the ANPC-2 drive distribution method (see Figure 3 for its drive distribution method), the internal tubes (S2, S3) operate at high frequency, while the other transistors (S1, S4, S5, S6) operate at the power supply frequency. In this case, the switching loss of the internal tubes is greater than that of the external tubes. Therefore, neither of these two drive distribution methods can achieve leveling of the switching losses of the devices.

[0026] As discovered through research, in the rectification process of the output voltage Vout at the midpoint of the phase bridge arm of the ANPC circuit (i.e., the AC side), which is 0→P→0→N→0, the switching tube that turns on first does not change the rectification path for the internal and external tubes. The current changes its flow path only when the switching tube that turns on later turns on. Therefore, there is no conduction loss in the conduction process of the switching tube that turns on first because there is no current, and a conduction loss is borne in the conduction process of the switching tube that turns on later because current flows. Similarly, a switching tube that turns off first bears an off-loss because current flows, and therefore, both the switching tube that turns off first and the switching tube that turns on later bear switching losses. Based on this principle, in order to actively equalize the switching losses of each device in the ANPC circuit, a drive distribution method with two modes is adopted, and the two defined modes are the stress-in mode, in which the internal tube bears the switching loss, and the stress-out mode, in which the external tube bears the switching loss. The dual-mode drive distribution method uses a pulse width modulation control method for carrier comparison to drive six switching tubes corresponding to stress-in mode and stress-out mode, respectively. For details, please refer to Figures 4 to 7. AB Vout is the AC output voltage, and V PVThis represents the voltage between the positive and negative electrodes on the DC side. Analyzing the positive half-period of the AC output voltage Vout as an example, and setting the modulated wave Sr and auxiliary modulated wave Sr' such that Sr' > Sr, as shown in Figure 4, when the modulated wave Sr is compared with the triangular wave carrier to generate the drive of switching tube S2, and the auxiliary modulated wave Sr' is compared with the triangular wave carrier to generate the drive of switching tube S1, in the current switching period, switching tube S1 turns on first and then off, and switching tube S2 turns on later and then off first (corresponding to the 0+In output state stage that appears twice in the figure), thus, stress-in mode. In this state, switching tube S2 bears the switching loss. Conversely, as shown in Figure 5, when the modulated wave Sr is compared with the triangular wave carrier to generate the drive for switching tube S1, and the auxiliary modulated wave Sr' is compared with the triangular wave carrier to generate the drive for switching tube S2, in the current switching period, switching tube S2 turns on first and then off, while switching tube S1 turns on later and then off first (corresponding to the 0+Out output state stage that appears twice in the diagram). Therefore, it belongs to the stress-out mode, and switching tube S1 bears the switching loss. In fact, by adjusting the ratio of stress-in mode and stress-out mode to, for example, 50% each, it is possible to equalize the switching losses between the internal and external tubes. Regarding the negative half-period situation of the AC output voltage Vout (shown in Figures 6 and 7), a similar analysis may be performed based on symmetry, and this has not been explained again.

[0027] However, in this dual-mode drive distribution method, the stress-in mode (e.g., the 0+In output state stage that appeared twice in Figure 4 and the 0-In output state stage that appeared twice in Figure 6) or the stress-out mode (e.g., the 0+Out output state stage that appeared twice in Figure 5 and the 0-Out output state stage that appeared twice in Figure 7) appeared twice symmetrically in each switching cycle, resulting in a large granularity for switching loss leveling over a single switching cycle. As the carrier proportionality decreases, this flaw becomes more pronounced, and the loss leveling performance further deteriorates.

[0028] This application provides a method for driving an ANPC circuit of a converter that achieves switching loss leveling of the device while reducing the granularity of switching loss leveling.

[0029] Referring to Figure 8, the method for driving the ANPC circuit of the converter includes the following steps. S101: Determine the output state switching sequence of the ANPC circuit of the converter, with the goal of enabling the ANPC circuit to bear switching losses by using the internal and external tubes respectively during two half-switching cycles of the switching period.

[0030] The switching period of the ANPC circuit includes two half-switching periods, during which the internal and external tubes of the ANPC circuit each bear the switching losses, thereby achieving equalization of the switching losses between the internal and external tubes.

[0031] Since the internal tube and the external tube each bear the switching losses, different switching combinations can be realized in zero-level output states, that is, S101 specifically includes the step of determining the zero-level output states of the output state switching sequence in two half-switching cycles within the switching cycle of the ANPC circuit, the zero-level output states including a first zero-level output state in which the internal tube bears the switching losses and a second zero-level output state in which the external tube bears the switching losses.

[0032] In actual application, the zero-level output state in the first half of the switching cycle may be set to include a first zero-level output state, and the zero-level output state in the second half of the switching cycle may be set to include a second zero-level output state, or the zero-level output state in the first half of the switching cycle may be set to include a second zero-level output state, and the zero-level output state in the second half of the switching cycle may be set to include a first zero-level output state. There is no limitation here, and it should be determined according to the specific application environment.

[0033] Within the positive half-cycle of the AC output voltage Vout, the first zero-level output state is denoted as 0+in, and in this state, the switching combination of the ANPC circuit is as follows: the first switching tube S1, the third switching tube S3, and the sixth switching tube S6 are ON, and the other switching tubes are OFF. The second zero-level output state is denoted as 0+out, and in this state, the switching combination of the ANPC circuit is as follows: the second switching tube S2, the third switching tube S3, and the sixth switching tube S6 are ON, and the other switching tubes are OFF.

[0034] During the negative half-cycle of the AC output voltage Vout, the first zero-level output state is denoted as 0-in, and in this case, the switching combination of the ANPC circuit is as follows: the second switching tube S2, the fourth switching tube S4, and the fifth switching tube S5 are ON, and the other switching tubes are OFF. The second zero-level output state is denoted as 0-out, and in this case, the switching combination of the ANPC circuit is as follows: the second switching tube S2, the third switching tube S3, and the fifth switching tube S5 are ON, and the other switching tubes are OFF.

[0035] S102: Based on the output state switching sequence, control signals for each switching tube in the ANPC circuit are generated and output.

[0036] The control signal for the switching tube is transmitted via the corresponding drive circuit, thereby enabling the drive of the corresponding switching tube.

[0037] According to the driving method of the ANPC circuit of the converter provided in this embodiment, the ANPC circuit can achieve leveling of the switching losses of the internal and external tubes through the above process, and by flexibly selecting between stress-in mode and stress-out mode for each half-switching cycle, the granularity of the switching loss leveling is reduced to half-switching cycles, resulting in a finer leveling effect and lower loss fluctuations.

[0038] Herein lies another drawback of the dual-mode drive distribution method, namely, that it only considers the leveling of switching losses and does not actively improve the leveling of on-state losses, since on-state losses and switching losses are of the same order. Therefore, this embodiment provides another method for driving an ANPC circuit, and based on the above embodiment, further includes the step of combining the objective of leveling the on-state losses borne by the internal tube before executing S101, which determines the output state switching sequence of the ANPC circuit. That is, S101 includes the step of determining the output state switching sequence of the ANPC circuit, combining the objective of leveling the on-state losses borne by the internal tube with the objective of having the ANPC circuit use the internal tube and the external tube, respectively, to bear the switching losses in two half-switching cycles of the switching period.

[0039] In this case, the specific process of S101 is as follows: the zero-level output state of the output state switching sequence in two half-switching cycles within the switching cycle of the ANPC circuit is determined, and this zero-level output state includes a first zero-level output state in which the internal tube bears the switching loss, a second zero-level output state in which the external tube bears the switching loss, and a third zero-level output state in which two parallel branches exist when the phase current flows into or out of the bridge arm.

[0040] Within the positive half-cycle of the AC output voltage Vout, the third zero-level output state is denoted as 0+, and in this state, the switching combination of the ANPC circuit is as follows: the third switching tube S3, the fifth switching tube S5, and the sixth switching tube S6 are in the ON state, and the other switching tubes are in the OFF state.

[0041] During the negative half-cycle of the AC output voltage Vout, the third zero-level output state is denoted as 0-, and in this case, the switching combination of the ANPC circuit is as follows: the second switching tube S2, the fifth switching tube S5, and the sixth switching tube S6 are in the ON state, and the other switching tubes are in the OFF state.

[0042] Referring to Figures 9 and 10, in the positive half-cycle of the AC output voltage of the ANPC circuit, the third zero-level output state has two parallel branches when the phase current flows into the bridge arm (see Figure 9). Therefore, the current flowing through the devices on each branch is half the phase current, which has a leveling effect on the on-state loss and reduces current stress. Referring to Figures 11 and 12, in the negative half-cycle of the AC output voltage of the ANPC circuit, the third zero-level output state has two parallel branches when the phase current flows out of the bridge arm (see Figure 12). Therefore, the current flowing through the devices on each branch is half the phase current, which has a leveling effect on the on-state loss and reduces current stress.

[0043] In this embodiment, by optimizing the switching combination when outputting a zero level, a zero-level parallel branch is constructed to actively level the on-state loss. In this case, the driving method of the ANPC circuit has the capability to level the switching loss as well as the capability to actively level the on-state loss.

[0044] As shown in Figure 1, in the ANPC circuit, the two external tubes are a first switching tube S1 connected to the DC positive electrode P and a fourth switching tube S4 connected to the DC negative electrode N, respectively; the two internal tubes are a second switching tube S2 connected between the first switching tube S1 and the AC side and a third switching tube S3 connected between the AC side and the fourth switching tube S4, respectively; and the two clamp tubes are a fifth switching tube S5 connected between the first switching tube S1 and the DC neutral point O and a sixth switching tube S6 connected between the DC neutral point O and the fourth switching tube S4, respectively. In this case, for each output state mentioned in the above embodiment, refer to the following.

[0045] That is, within the positive half-cycle of the AC output voltage Vout of the ANPC circuit, in the first zero-level output state 0+in, the first switching tube S1, the third switching tube S3, and the sixth switching tube S6 are ON, and the other switching tubes are OFF; in the second zero-level output state 0+out, the second switching tube S2, the third switching tube S3, and the sixth switching tube S6 are ON, and the other switching tubes are OFF; in the third zero-level output state 0+, the third switching tube S3, the fifth switching tube S5, and the sixth switching tube S6 are ON, and the other switching tubes are OFF; and in the positive level output state P, the first switching tube S1, the second switching tube S2, and the sixth switching tube S6 are ON, and the other switching tubes are OFF.

[0046] In the negative half-cycle of the AC output voltage Vout of the ANPC circuit, in the first zero-level output state 0-in, the second switching tube S2, the fourth switching tube S4, and the fifth switching tube S5 are ON, and the other switching tubes are OFF; in the second zero-level output state 0-out, the second switching tube S2, the third switching tube S3, and the fifth switching tube S5 are ON, and the other switching tubes are OFF; in the third zero-level output state 0-, the second switching tube S2, the fifth switching tube S5, and the sixth switching tube S6 are ON, and the other switching tubes are OFF; and in the negative level output state N, the third switching tube S3, the fourth switching tube S4, and the fifth switching tube S5 are ON, and the other switching tubes are OFF.

[0047] In other words, this embodiment designs the switching state combinations shown in Table 1, specifically illustrating the switching states of switching tubes S1 to S6 in eight different bridge arm output states, where 1 is ON and 0 is OFF.

[0048] [Table 1]

[0049] Table 1 includes the following six zero-level output states: O+in: The first zero-level output state where the internal tube bears the switching losses during the positive half-cycle of the AC output voltage; O+out: A second zero-level output state where the external tube bears the switching losses during the positive half-cycle of the AC output voltage; O+: The third zero-level output state of the positive half-cycle of the AC output voltage; O-in: The first zero-level output state where the internal tube bears the switching losses during the negative half-cycle of the AC output voltage; O-out: A second zero-level output state where the external tube bears the switching losses during the negative half-cycle of the AC output voltage; O-: The third zero-level output state of the negative half-cycle of the AC output voltage.

[0050] In all six zero-level output states, the output level of the bridge arm is 0; however, because the rectifier circuits are different, the corresponding switching losses and on-state losses differ. By combining the six zero-level output states, the switching losses and on-state losses can be equalized.

[0051] Regarding switching losses, when a 0 level is output in a positive half-cycle, selecting O+in means the internal tube bears the switching loss; when a 0 level is output in a positive half-cycle, selecting O+out means the external tube bears the switching loss; when a 0 level is output in a negative half-cycle, selecting O-in means the internal tube bears the switching loss; and when a 0 level is output in a negative half-cycle, selecting O-out means the external tube bears the switching loss.

[0052] Regarding the on-state loss, when outputting a 0 level in a positive half-cycle, O+ is selected. Regarding the phase current path, as shown in Figures 9 and 10, when the phase current flows into the bridge arm, there are two parallel current branches. Therefore, the current flowing through the devices on each branch is half the phase current, which has a leveling effect on the on-state loss and reduces current stress. Similarly, when outputting a 0 level in a negative half-cycle, O- is selected. Regarding the phase current path, as shown in Figures 11 and 12, when the phase current flows out of the bridge arm, there are two parallel current branches. Therefore, the current flowing through the devices on each branch is half the phase current, which has a leveling effect on the on-state loss and reduces current stress.

[0053] Based on the concept of leveling switching losses and on-state losses by different zero-level output states, the following drive distribution method is determined. Specifically, in the positive half-cycle of the AC output voltage, an output state switching sequence of O+→O+in, O+out→P→O+out, or O+in→O+ is adopted, and in the negative half-cycle of the AC output voltage, an output state switching sequence of O-→O-in, O-out→P→O-out, or O-in→O- is adopted, and then the drive of switching tubes S1 to S6 is determined according to each output state in Table 1. That is, based on the above embodiment, this embodiment gives the following as some specific examples of output state switching sequences. (1) Within the positive half-cycle of the AC output voltage Vout of the ANPC circuit, the output state switching sequence is as follows: third zero-level output state, first zero-level output state, positive level output state, second zero-level output state, and third zero-level output state appear in that order, i.e., 0+ → 0+in → P → 0+out → 0+. (2) Within the positive half-cycle of the AC output voltage Vout of the ANPC circuit, the output state switching sequence is as follows: third zero-level output state, second zero-level output state, positive level output state, first zero-level output state, and third zero-level output state appear in that order, i.e., 0+ → 0+out → P → 0+in → 0+. (3) In the negative half-period of the AC output voltage Vout of the ANPC circuit, the output state switching sequence will occur in the following order: third zero-level output state, first zero-level output state, negative level output state, second zero-level output state, and third zero-level output state, i.e., 0-→0-in→N→0-out→0-. (4) In the negative half-period of the AC output voltage Vout of the ANPC circuit, the output state switching sequence is as follows: third zero-level output state, second zero-level output state, negative level output state, first zero-level output state, and third zero-level output state appear in that order, i.e., 0-→0-out→N→0-in→0-.

[0054] In the driving method for the ANPC circuit provided by this embodiment, both the zero-level switching combination and the zero-level flywheel loop differ from those of the prior art. Specifically, by setting two zero-level output states, 0+ and 0-, in the output state switching sequence, the leveling of on-state losses is actively improved, and by flexibly selecting between 0+in or 0+out and 0-in or 0-out, the leveling of switching losses is actively improved, thereby reducing the granularity of switching loss leveling.

[0055] Figure 13 illustrates a selectable and specific output state switching sequence, 0+→0+in→P→0+out→0+, for one switching cycle of the bridge arm output. In this case, the switching loss is borne by the internal tube during the first half of the switching cycle and by the external tube during the second half, resulting in a finer granularity of switching loss distribution.

[0056] Based on the above embodiment, preferably, S102 in the driving method of the ANPC circuit specifically includes a step of generating and outputting a control signal for each switching tube based on the on / off state of each switching tube in the ANPC circuit in each output state in the output state switching sequence, that is, the pulses of each switching tube can be directly obtained according to the bridge arm output voltage comparison table 1, and the implementation method is more flexible than that of the two-mode drive distribution method.

[0057] Alternatively, step S102 may further include a step of generating and outputting control signals for each switching tube of the ANPC circuit by employing a carrier comparison method, with the aim of realizing an output state switching sequence. Figure 13 illustrates the process of realizing the output state switching sequence 0+→0+in→P→0+out→0+ using a carrier comparison method.

[0058] The specific implementation of S102 can be determined according to its applicable environment, and is not limited here; all fall within the scope of protection of this application.

[0059] Other embodiments of this application further provide a converter comprising a main circuit and a control device, the main circuit comprising at least one ANPC circuit, the structure of which is shown in Figure 1, and specifically comprising six switching tubes (S1 to S6 in the drawing), each switching tube comprising a corresponding flywheel diode (D1 to D6 in the drawing), the first switching tube S1 to the fourth switching tube S4 being connected in series sequentially, the other end of the first switching tube S1 being connected to the DC positive electrode P of the ANPC circuit, the other end of the fourth switching tube S4 being connected to the DC negative electrode N of the ANPC circuit, and the first switching tube S1 and the fourth switching tube S4 each comprising two external tubes of the ANPC circuit The connection point between the second switching tube S2 and the third switching tube S3 is connected to the AC side of the ANPC circuit (its output voltage is Vout), and the second switching tube S2 and the third switching tube S3 each function as two internal tubes of the ANPC circuit. The connection point between the first switching tube S1 and the second switching tube S2 is connected to the DC side neutral point O of the ANPC circuit via the fifth switching tube S5, and the connection point between the third switching tube S3 and the fourth switching tube S4 is connected to the DC side neutral point O of the ANPC circuit via the sixth switching tube S6, and the fifth switching tube S5 and the sixth switching tube S6 each function as two clamp tubes of the ANPC circuit.

[0060] The main circuit comprises only one ANPC circuit to constitute a single-phase converter. Alternatively, the main circuit comprises three ANPC circuits, the DC sides of each ANPC circuit are connected in parallel, and the AC sides of each ANPC circuit each constitute one phase of the AC side of the main circuit to constitute a three-phase converter. Furthermore, the converter may be an inverter, a rectifier, or a device comprising at least two conversion circuits, one of which is an ANPC circuit. There are no limitations, and all fall within the scope of protection of this application.

[0061] The main circuit is controlled by a control device, which executes the method for driving the ANPC circuit of the converter described in any of the above embodiments. The specific process and principle of the method for driving the ANPC circuit can be found in the above embodiments, and no further explanation is provided here.

[0062] The control device, by executing the driving method of the ANPC circuit, can adjust the on / off order of the switching tubes to achieve leveling of the switching losses between the internal and external tubes. By selecting and turning on the appropriate switching tube, it can achieve leveling of the on-state losses. Thus, the converter has the capability to level switching losses, as well as the capability to actively level on-state losses. Furthermore, the granularity of the leveling of switching losses becomes smaller, resulting in smaller loss fluctuations.

[0063] Similar or identical parts between the embodiments of this specification can be referenced to one another, while each embodiment primarily describes the differences from the others. In particular, since the systems or system embodiments are basically similar to the method embodiments, their description is simple, and relevant parts can be referenced to the descriptions of the method embodiments. The systems and system embodiments described above are illustrative only, and the units described as individual components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one place or distributed across multiple network units. Depending on the actual needs, some or all of these modules can be selected to achieve the objectives of the solutions of these embodiments. Those skilled in the art will be able to understand and implement these without performing work commensurate with inventive step.

[0064] As will be further aware to those skilled in the art, each exemplary unit and algorithmic step described in combination with the embodiments disclosed herein is implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability between hardware and software, each exemplary combination and step is generally described in the above description according to its function. Whether these functions are performed in hardware form or software form depends on the specific application and design constraints of the technical proposal. Those skilled in the art may implement the described functions using different methods for each specific application, but such implementations should not be considered beyond the scope of the invention.

[0065] With respect to the above descriptions of the disclosed embodiments, the features described in each embodiment herein may be substituted or combined with each other so that a person skilled in the art can realize or use the present invention. Several modifications to these embodiments are obvious to a person skilled in the art, and the general principles defined herein may be realized in other embodiments without departing from the spirit or scope of the invention. Accordingly, the present invention is not limited to these embodiments described herein and fits the broadest scope that is consistent with the principles and novel features disclosed herein.

Claims

1. A method for driving the ANPC circuit of a converter, With the goal of enabling the ANPC circuit of the converter to bear switching losses by using the internal tube and the external tube, respectively, during two half-switching cycles of the switching period, the steps include determining the output state switching sequence of the ANPC circuit, The steps include generating and outputting control signals for each switching tube in the ANPC circuit based on the output state switching sequence, Includes, With the goal of enabling the ANPC circuit of the converter to bear switching losses by using the internal tube and the external tube, respectively, within two half-switching cycles of the switching period, the step of determining the output state switching sequence of the ANPC circuit is: The step includes determining the zero-level output state of the output state switching sequence during two half-switching cycles within the switching cycle of the ANPC circuit, The aforementioned zero-level output states include a first zero-level output state in which the internal tube bears the switching loss, a second zero-level output state in which the external tube bears the switching loss, and a third zero-level output state in which two parallel branches exist when phase current flows into or out of the bridge arm. Within the positive half-cycle of the AC output voltage of the aforementioned ANPC circuit, the third zero-level output state occurs when phase current flows into the bridge arm, and there are two parallel branches. A method for driving an ANPC circuit of a converter, characterized in that, in the negative half-cycle of the AC output voltage of the ANPC circuit, the third zero-level output state has two parallel branches when the phase current flows out from the bridge arm.

2. In the aforementioned ANPC circuit, the two external tubes are a first switching tube connected to the positive terminal of the DC side and a fourth switching tube connected to the negative terminal of the DC side, the two internal tubes are a second switching tube connected between the first switching tube and the AC side and a third switching tube connected between the AC side and the fourth switching tube, and the two clamp tubes are a fifth switching tube connected between the first switching tube and the DC side neutral point and a sixth switching tube connected between the DC side neutral point and the fourth switching tube. Within the positive half-cycle of the AC output voltage of the ANPC circuit, in the first zero-level output state, the first switching tube, the third switching tube, and the sixth switching tube are in the ON state, and the other switching tubes are in the OFF state. During the negative half-cycle of the AC output voltage of the ANPC circuit, in the first zero-level output state, the second switching tube, the fourth switching tube, and the fifth switching tube are in the ON state, while the other switching tubes are in the OFF state. A method for driving the ANPC circuit of the converter according to feature 1.

3. In the aforementioned ANPC circuit, the two external tubes are a first switching tube connected to the positive terminal of the DC side and a fourth switching tube connected to the negative terminal of the DC side, the two internal tubes are a second switching tube connected between the first switching tube and the AC side and a third switching tube connected between the AC side and the fourth switching tube, and the two clamp tubes are a fifth switching tube connected between the first switching tube and the DC side neutral point and a sixth switching tube connected between the DC side neutral point and the fourth switching tube. Within the positive half-cycle of the AC output voltage of the ANPC circuit, in the second zero-level output state, the second switching tube, the third switching tube, and the sixth switching tube are in the ON state, and the other switching tubes are in the OFF state. During the negative half-cycle of the AC output voltage of the ANPC circuit, in the second zero-level output state, the second switching tube, the third switching tube, and the fifth switching tube are in the ON state, while the other switching tubes are in the OFF state. A method for driving the ANPC circuit of the converter according to feature 1.

4. In the aforementioned ANPC circuit, the two external tubes are a first switching tube connected to the positive terminal of the DC side and a fourth switching tube connected to the negative terminal of the DC side, the two internal tubes are a second switching tube connected between the first switching tube and the AC side and a third switching tube connected between the AC side and the fourth switching tube, and the two clamped tubes are a fifth switching tube connected between the first switching tube and the DC side neutral point and a sixth switching tube connected between the DC side neutral point and the fourth switching tube. Within the positive half-cycle of the AC output voltage of the ANPC circuit, in the third zero-level output state, the third switching tube, the fifth switching tube, and the sixth switching tube are in the ON state, and the other switching tubes are in the OFF state. During the negative half-cycle of the AC output voltage of the ANPC circuit, in the third zero-level output state, the second switching tube, the fifth switching tube, and the sixth switching tube are in the ON state, while the other switching tubes are in the OFF state. A method for driving the ANPC circuit of the converter according to feature 1.

5. The output state switching sequence is as follows: The aforementioned third zero-level output state, the aforementioned first zero-level output state, a positive or negative level output state, the aforementioned second zero-level output state, the aforementioned third zero-level output state, or The aforementioned third zero-level output state, the aforementioned second zero-level output state, a positive level or negative level output state, the aforementioned first zero-level output state, the aforementioned third zero-level output state, A method for driving the ANPC circuit of a converter according to claim 1, characterized in that the following appear in order.

6. The step of generating and outputting control signals for each switching tube of the ANPC circuit based on the output state switching sequence is as follows: A step of generating and outputting a control signal for each switching tube based on the on / off state of each switching tube in the ANPC circuit in each output state in the output state switching sequence, or With the goal of realizing the aforementioned output state switching sequence, the method includes a step of generating and outputting control signals for each switching tube in the ANPC circuit using a carrier comparison method. A method for driving the ANPC circuit of the converter according to feature 1.

7. A method for driving the ANPC circuit of a converter, With the goal of enabling the ANPC circuit of the converter to bear switching losses by using the internal tube and the external tube, respectively, during two half-switching cycles of the switching period, the steps include determining the output state switching sequence of the ANPC circuit, The steps include generating and outputting control signals for each switching tube in the ANPC circuit based on the output state switching sequence, Includes, With the goal of enabling the ANPC circuit of the converter to bear switching losses by using the internal tube and the external tube, respectively, during two half-switching cycles of the switching period, the step of determining the output state switching sequence of the ANPC circuit is: The step includes determining the zero-level output state of the output state switching sequence during two half-switching cycles within the switching cycle of the ANPC circuit, The aforementioned zero-level output state includes a first zero-level output state in which the internal tube bears the switching loss, and a second zero-level output state in which the external tube bears the switching loss, respectively. In the aforementioned ANPC circuit, the two external tubes are a first switching tube connected to the positive terminal of the DC side and a fourth switching tube connected to the negative terminal of the DC side, the two internal tubes are a second switching tube connected between the first switching tube and the AC side and a third switching tube connected between the AC side and the fourth switching tube, and the two clamp tubes are a fifth switching tube connected between the first switching tube and the DC side neutral point and a sixth switching tube connected between the DC side neutral point and the fourth switching tube. Within the positive half-cycle of the AC output voltage of the ANPC circuit, in the first zero-level output state, the first switching tube, the third switching tube, and the sixth switching tube are ON, and the other switching tubes are OFF; in the second zero-level output state, the second switching tube, the third switching tube, and the sixth switching tube are ON, and the other switching tubes are OFF. A method for driving an ANPC circuit of a converter, characterized in that, during the negative half-cycle of the AC output voltage of the ANPC circuit, in the first zero-level output state, the second switching tube, the fourth switching tube, and the fifth switching tube are ON, and the other switching tubes are OFF, and in the second zero-level output state, the second switching tube, the third switching tube, and the fifth switching tube are ON, and the other switching tubes are OFF.

8. It is a converter, Including the main circuit and control device, The main circuit includes at least one ANPC circuit, The main circuit is controlled by the control device, and the control device performs the method for driving the ANPC circuit of the converter according to any one of claims 1 to 7. A converter characterized by the following features.

9. The aforementioned ANPC circuit includes six switching tubes, The first to fourth switching tubes are connected in series in sequence. The other end of the first switching tube is connected to the DC positive terminal of the ANPC circuit, and the other end of the fourth switching tube is connected to the DC negative terminal of the ANPC circuit, and the first switching tube and the fourth switching tube each function as two external tubes of the ANPC circuit. The connection point between the second switching tube and the third switching tube is connected to the AC side of the ANPC circuit, and the second and third switching tubes each function as two internal tubes of the ANPC circuit. The connection point between the first switching tube and the second switching tube is connected to the DC neutral point of the ANPC circuit via the fifth switching tube, the connection point between the third switching tube and the fourth switching tube is connected to the DC neutral point of the ANPC circuit via the sixth switching tube, and the fifth and sixth switching tubes each function as two clamp tubes of the ANPC circuit. The converter according to feature 8.

10. The main circuit includes three of the ANPC circuits, The DC side of each ANPC circuit is connected in parallel, and the AC side of each ANPC circuit is one phase of the AC side of the main circuit. The converter according to feature 8.

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